Reactor pH Research Articles

Artificial intelligence-driven control for enhancing carbon dioxide-based wastewater pH regulation in tubular reactor

Alkaline wastewater treatment using carbon dioxide can reduce chemical costs and provide a safer alternative to traditional methods. However, complex gas-liquid reactions and narrow operating pH ranges present challenges. This research develops an artificial intelligence-driven control system for treating alkaline wastewater using carbon dioxide in a bench-scale tubular reactor. The proposed control system employs an inverse neural network to regulate the carbon dioxide gas based on the desired setpoint, along with a Smith predictor and a linear controller to compensate for natural delays, model mismatches, and pH disturbances. The inverse neural controller was trained using experimental data from a bench-scale reactor pH treatment of synthetic alkaline wastewater and verified on real influent from an electroplating wastewater treatment plant. The results show that the proposed method efficiently enforces the desired reactor outlet pH setpoint with up to 51.36% faster settling time than a proportional-integral controller while improving pH-adjusting efficiency by 72.24%.

Ideal performance assessment of non-recirculating anaerobic fluidized bed reactors treating low to high strength organic loads with low retention time

This study investigated the ideal performance of non-recirculating Anaerobic Fluidized Bed Reactors (AnFBRs) for treating organic wastewater of varying strengths under low Hydraulic Retention Time (HRT). Four 4.58 L AnFBRs were used to treat synthetic wastewater with an Organic Loading Rate (OLR) ranging from 4.50 to 40.11 gCOD/L-d, and HRT between 1.1 and 4.4 hours. The AnFBRs achieved high removal efficiencies ranging from 83 % to 96 % at steady state, except during the organic shock load, which reduced removal performance to 12 %. Shortened HRT conditions led to a decreasing trend in reactor pH due to an incomplete anaerobic cycle. The modified Stover-Kincannon model estimated the maximum substrate utilization rate of AnFBR's to be 196.08 gCOD/L-d, with a correlation coefficient of 0.98. Under shortended HRT, microbial diversity analysis identified predominant non-filamentous bacterial families, such as Streptococcaceae and Veillonellaceae, which collaborate during biofilm development in anaerobic environments. It was suggested that the porous media provided secure attachment sites for the biomass growth and biofilm formation under shock load and high shear force conditions. While these results offer valuable insights, further studies are needed to confirm these findings and enhance the understanding of the use porous media in non-recirculating AnFBRs.

Production of ammonium nitrate for nitrogen recovery in a single bioreactor operating at pH 3

Ammonium nitrate (AN), i.e. NH4NO3, is extensively utilized in agricultural, mining, and civil construction sectors, with an annual production of approximately 16 million tons. Although the biological nitrification processes has been proven to be an important alternative to overcome the intensive energy consumption of the conventional chemical process for AN production, it necessitates ample chemical input for stable performance. This study marks the first demonstration of stable AN production from ammonium-rich wastewater employing a purely microbial-derived one-stage process, without the need for external chemical addition. This process functioned through an acidophilic ammonia-oxidizing bacteria (AOB), i.e., Candidatus (Ca.) Nitrosoglobus, which oxidized the ammonium in the feed to nitrite while simultaneously reducing the reactor pH to 3.2−3.4. Under these pH conditions, nitrite was chemically oxidized to nitrate with the provision of oxygen. Long-term bioreactor operation (>230 days) revealed consistent AN production from high ammonium wastewater at a nitrogen loading rate of 0.15 kg N/m3/d. Batch tests revealed that microbial ammonium oxidation was the rate-determining step in the overall AN production process. Further microbial enrichment and process optimization can enhance the microbial ammonium oxidation rate. In summary, the proposed acidic one-stage bioprocess presents a promising avenue for AN production from ammonium-rich wastewater.

Multiscale effects of radial mixing on mixotrophic microalgal growth and macromolecular synthesis in tubular bubble-column photobioreactors

Extremophillic microalga Chlorella sorokiniana is grown mixotrophically in a 5 L externally-illuminated tubular bubble-column photobioreactor with an external light intensity of 10,500 lx (≈195 μmol-photons.m−2.s−1) at atmospheric (0.04 %), 1 %, 2 %, 3 %, 4 %, and 5 % CO2 concentrations, with acetic acid and urea as the organic carbon and nitrogen sources, respectively, for 6–8 days. Two different setups are employed: one permits axial air flow, and another promotes radial mixing of algal particles, dissolved CO2 and nutrients along with axial sparging. We show that radial mixing increases biomass yields by reducing both photo-limitation and photo-inhibition up to CO2 concentrations <3 %, above which substrate (CO2) inhibition necessitates lower reactor mixing. Radial mixing increases the lipid yield from 1.06 and 1.61 g/L to 1.27 and 1.78 g/L at 2 % and 3 % CO2, respectively, in nitrogen-limited cases, resulting in a 10–20 % increase. We show that complete reactor mixing, facilitated by the dual effects of branched (radial) and axial sparger, is preferred only in the absence of substrate (CO2) inhibition. Subsequently, we stratify the tubular photobioreactor design strategy into two regimes based on CO2 inlet concentrations. In one regime (for inlet CO2 < 3 %), we recommend the deployment of branched sparger to facilitate both radial and axial mixing simultaneously, thereby creating a well-mixed reactor at lower CO2 concentrations. In the other regime (for inlet CO2 > 3 %), axial sparging alone is recommended since complete mixing of CO2 increases substrate inhibition by reducing the reactor pH below 7.5.

Enhancing scalability and economic viability of lignocellulose-derived biofuels production through integrated pretreatment and methanogenesis arrest

The pursuit of affordable biofuels necessitates continuous refinement of valorization strategies, focusing on cost-effective feedstocks, accessible bioprocessing, and high-quality products. High energy input required during various stages, including pretreatment, post-pretreatment, and methanogenesis arrest, impeded the economic lignocellulose-derived biofuels production from anaerobic digestion (AD). Addressing this challenge, an upstream process integrating synergistic alkali pretreatment and arrested AD was proposed. Results demonstrated that an optimum reactor pH 10 yielded a volatile fatty acids (VFA) titer of 3.6 gCOD/L, only 23% lower than using methanogenesis inhibitor. The study further explored the interplay between initial pH, cell viability/functionality, and VFA production by assessing cell viability and cell population demographics. This integrated approach demonstrated a VFA yield of 364 gVFA/kgTSsubstrate at a cost of just USD 0.2/kgVFA, encompassing post-pretreatment and methanogenesis arrest, which underscores the viability of combining pretreatment and methanogenesis arrest for cost effective and scalable biofuels production.

Adaptation of anammox process for nitrogen removal from acidic nitritation effluent in a low pH moving bed biofilm reactor.

Acidic partial nitritation (PN) has emerged to be a promisingly stable process in wastewater treatment, which can simultaneously achieve nitrite accumulation and about half of ammonium reduction. However, directly applying anaerobic ammonium oxidation (anammox) process to treat the acidic PN effluent (pH 4-5) is susceptible to the inhibition of anammox bacteria. Here, this study demonstrated the adaptation of anammox process to acidic pH in a moving bed biofilm reactor (MBBR). By feeding the laboratory-scale MBBR with acidic PN effluent (pH=4.6±0.2), the pH of an anammox reactor was self-sustained in the range of pH 5-6. Yet, a high total nitrogen removal efficiency of over 80% at a practical loading rate of up to 149.7±3.9mg N/L/d was achieved. Comprehensive microbial assessment, including amplicon sequencing, metagenomics, cryosection-FISH, and qPCR, identified that Candidatus Brocadia, close to known neutrophilic members, was the dominant anammox bacteria. Anammox bacteria were found present in the inner layer of thick biofilms but barely present in the surface layer of thick biofilms and in thin biofilms. Results from batch tests also showed that the activity of anammox biofilms could be maintained when subjected to pH 5 at a nitrite concentration of 10mg N/L, whereas the activity was completely inhibited after disturbing the biofilm structure. These results collectively indicate that the anammox bacteria enriched in the present acidic MBBR could not be inherently acid-tolerant. Instead, the achieved stable anammox performance under the acidic condition is likely due to biofilm stratification and protection. This result highlights the biofilm configuration as a useful solution to address nitrogen removal from acidic PN effluent, and also suggests that biofilm may play a critical role in protecting anammox bacteria found in many acidic nature environments.

Selective assembly of microbe on patterned porous interfaces as potential membrane reactors for enhanced biodegradation of phenol

The carriers of membrane reactors faced challenges of high cost, and decrease of adsorption and efficiency on the long-term use for wastewater treatment. A facile method to prepare a novel membrane reactor by assembly of microbe on porous interfaces via breath figure for efficient biodegradation of phenol was developed. After the preparation and localized modification of porous interfaces, microbe was selectively incorporated into the patterned cavities, with an extremely high loading amount of 1.56 × 108 /cm2. A much better degradation rate (23.08 mg·L−1·h−1) was achieved in the membrane reactor than free cells (15.7 mg·L−1·h−1), which was improved nearly 50%. The high activity of phenol hydroxylase and catechol 1,2-dioxygenase, and low level of SOD, CAT and POD gave rise to the efficient phenol degradation rate in membrane reactor. Moreover, a good stability under a wider pH (3−8) of membrane reactor presented the degradation efficiency 5–8 times higher than free microbe. Further, at the stress of heavy metal ions, an excellent treatment of phenol was still existed, enhancing the degradation efficiency 3–6 times than free microbe. This strategy provides a new route on the preparation of a cheap, highly efficient and stable membrane reactor, demonstrating its potential on environment and biomedicine.

Effect of pH on lactic acid fermentation of food waste using different mixed culture inocula

AbstractBACKGROUNDIncreasing amounts of food waste (FW) have become a critical problem in the last few decades. Sustainable methods to limit the impact of FW on the environment are required. FW valorisation through lactic acid (LA) fermentation can assist by producing a valuable commodity from a cheap substrate. LA is a chemical with increasing market potential, it is used in several industrial sectors, and it is the main component of polylactic acid bioproducts.RESULTSThe role of pH on LA production from FW was tested with three anaerobic inocula and a control with solely FW. The most suitable condition for LA production was at pH &lt; 4. The best results in terms of final LA concentration (1.8 gCOD L–1), yield (224 mgCOD/gVS), and COD conversion (50%) were found in uncontrolled pH conditions with no external inoculum addition. FW already has a good abundance of LA bacteria that are responsible for lactate production. Among the external inocula supplied, primary sludge best enabled LA accumulation at a high concentration (1.3 g COD L–1) and yield (167 mgCOD/gVS).CONCLUSIONThis study demonstrates that the reactor pH is a key factor to stimulate LA acid fermentation and its accumulation. Under acidic conditions, LA accumulated in the system instead of being converted to volatile fatty acids (VFAs); this was likely due to the inhibition of the microbial community responsible for VFAs production. Uncontrolled pH condition impacts positively the overall fermentation cost since the alkalinizing agents used to keep pH neutral are not required and simplifies the downstream processes for LA extraction and purification. © 2021 Society of Chemical Industry (SCI).

Effects of the reactor volumetric ratio and recycle ratio on the methane and energy productivity of a three-step anaerobic sequencing batch reactor (3S-ASBR) treating ethanol wastewater

A new three-step anaerobic sequencing batch reactor (3S-ASBR) was developed to enhance methane productivity and energy yield by varying the reactor volumetric and recycle ratios. The pH of the first reactor (R1) was maintained at 5.5, whereas that of the others (R2/R3) was not controlled. The effluent from R3 was recirculated to R1 to amplify the alkalinity and lessen the NaOH quantity for pH regulation. The 3S-ASBR was continually operated to attain a steady state at a moderate COD loading rate (10 kg/m3d) with different reactor volumetric ratios under 37 °C, a fixed total liquid volume of 30 L and a constant recycle ratio of unity. A R1:R2:R3 volumetric ratio of 1:1.5:5 gave the highest COD reduction (90%) and yielded 343 mL CH4/g COD applied with an overall energy extraction efficiency of up to 66%. This volumetric ratio corresponded well to the generation time ratio of the microbes involved in the hydrolysis/acidogenesis, acetogenesis, and methanogenesis steps which can be applied to scale up both 3S-ASBR and three-step/stage upflow anaerobic sludge blanket (3S-UASB) systems. The low pH level (5.5) in R1 was responsible for maintaining adequate amounts of all micronutrients in the system, causing both high microbial concentrations and activities. This was because the lower the solution pH, the higher the fraction of produced H2S to be in the gaseous phase, causing the lower the amounts of micronutrients to be precipitated chemically.

Effect of Different Parameters of The Biological Processes on The Specific Growth Rate of Nitrifying Bacteria by Means of Mathematical Models

In this study, the biological removal of nitrogen from wastewater with relatively high ammonium concentration is investigated by modelling and simulation. Specifically, the nitrification process, means the oxidation of ammonium to nitrate, which is catalysed by two types of bacteria, namely ammonium-oxidising bacteria (AOB) and nitrite-oxidising bacteria (NOB). In wastewater treatment, ammonia oxidation lowers the pH of wastewaters with in relation to total ammonia limited alkalinity. By reducing the pH, ammonia oxidation often stops just below pH 6-6.5. On the other hand, nitrification has been found to occur even at low pH in reactors that process human urine, although it was not clear which species of bacteria are involved. Against this background, this research used different mathematical models of ammonia-oxidising bacteria (AOB). The aim is to estimate those sludge residence times as a function of pH that can achieve complete nitrification of the NH3-N load in the influent. Quantity of base that should be dosed to the system and the capacity of the bioreactor have been calculated using estimated data. The values obtained have also been compared with the values from literature.

Continuous treatment of an azo dye based on a combined ZVI/photo-Fenton setup. Process modelling by response surface methodology

The performance of a continuous system that sequentially couples a column filled with zero-valent iron with a photo-Fenton reactor was evaluated under mild acidic conditions. Studies were conducted to evaluate the better coupling strategy between each treatment module and to analyze the effects of several operational parameters on the system behaviour. The azo dye Acid Black 1 was chosen as model pollutant. Decolourization degrees and decreases of TOC values were used for the evaluation of the treatment performance under different conditions; whereas steady state concentrations of Fe(II), Fe(III) and H2O2 together with spectral features in the UV–vis region were analysed to elucidate mechanistic issues. The response surface methodology approach based on a central composite design was used to evaluate and model the effects of key factors on the decolourization degrees.Results show that the spatial separation between the ZVI and H2O2 may lead to substantial improvements of treatment efficiencies provided that configurations involving recirculation loops are avoided. Besides, a strict and continuous pH control during the oxidative stage is critical for obtaining a stable operation and acceptable decolourization efficiencies through the coupled system. The simple parameters developed from UV–vis spectra allowed monitoring the extent of reductive and oxidative transformation pathways. In addition, the statistical analysis shows that reactor pH and hydraulic residence time are the key factors influencing the system response, whereas initial pH and added oxidant concentration are much less significant. The conclusions drawn are relevant from a technological viewpoint since allow a rational design of cost-effective treatments.

Methanol-Based Chain Elongation with Acetate to n-Butyrate and Isobutyrate at Varying Selectivities Dependent on pH

Biomass fermentation technologies offer alternative methods to produce platform chemicals that currently originate from fossil sources. This research showed that an enriched microbiome was capable to produce iso-butyric acid via methanol based chain elongation of acetate. A long term continuous reactor experiment showed that the selectivity for isobutyrate (i-C4) and/or n-butyrate (n-C4) could be reversibly adjusted by changing the reactor pH. A reactor pH of 6.75 led to formation of (carbon per total carbon of products) of 0.78 n-C4 and 0.024 i-C4, whereas a reactor pH of 5.2 led to a selectivity of 0.25 n-C4 and 0.63 i-C4 . This shift in product spectrum was also represented by a shift in microbial composition. The results suggest that an Eubacterium genus is responsible for the formation of n-C4, whereas a Clostridium luticellarii strain is responsible for the formation of a mixture of i-C4 and n¬¬-C4. The formation of n and i-C4 at a low pH was observed to be coupled according to the thermodynamics of isomerization. At a reactor pH of 5.5 and 5.2 the product ratio of i-C4:n-C4 approached the ratio of 0.684 i-C4 : 0.316 n-C4, which is the theoretical ratio that would be achieved when i-C4 and n-C4 would be formed at amounts determined by the equilibrium of isomerization. Various batch experiments at pH 5.5 and 5.2 confirmed that addition of either n-C4 or i-C4 at the start of the batch would immediately lead to the formation of the other butyrate component. Moreover, batch experiments performed at pH 6.5 immediately produced mainly n-C4 and led to the development of a completely different microbiome. The imposed pH as a strong selective pressure can immediately facilitate changes in product selectivities for n-C4 and i-C4 during methanol based chain elongation of acetate.

Fe3+-NTA as iron source for solar photo-Fenton at neutral pH in raceway pond reactors

This work presents, for the first time, a kinetic study of the solar photo-Fenton process at neutral pH mediated by the Fe3+-NTA complex (molar ratio 1: 1) applied to remove contaminants of emerging concern (CECs). To this end, wastewater treatment plant (WWTP) secondary effluents were treated in a raceway pond reactor (RPR) at pilot plant scale with 0.1 mM Fe3+-NTA and 0.88 mM H2O2 under average solar UVA irradiance of 35 W/m2. Sulfamethoxazole and imidacloprid, at 50 μg/L of initial concentration each, were selected as model CECs. Up to 40% of the sum of both model CECs was removed from simulated WWTP effluent by the Fe3+-NTA Fenton-like process, and >80% was removed by solar photo-Fenton. The effect of liquid depth in the reactor was evaluated, showing an increase of the treatment capacity from 12 mg CEC/m2·h to 18 mg CEC/m2·h when liquid depth increased from 5 to 15 cm. Afterwards, these results were validated with real WWTP effluents and compared with the results obtained with the Fe3+-EDDS complex under the same operating conditions. The same CEC removal rates were obtained with Fe3+-NTA and Fe3+-EDDS at 5 cm of liquid depth (kinetic constants of 0.110 min−1 and 0.046 min−1 for sulfamethoxazole and imidacloprid, respectively). Conversely, at 15 cm of liquid depth, the degradation rates were lower with Fe3+-NTA (kinetic constants of 0.034 min−1 for sulfamethoxazole and 0.017 min−1 for imidacloprid), whereas with Fe3+-EDDS the values were 0.076 min−1 and 0.047 min−1 for sulfamethoxazole and imidacloprid, respectively. Regarding process cost estimation, the use of NTA as iron chelate for solar photo-Fenton at neutral pH at pilot plant scale resulted very cost-effective (0.13–0.14 €/m3) in comparison with the use of EDDS (0.46–0.48 €/m3) at the two liquid depths tested.

A new strategy to recover from volatile fatty acid inhibition in anaerobic digestion by photosynthetic bacteria

The accumulation of volatile fatty acids (VFAs) can decrease reactor pH and inhibit methane-producing process. For the first time, photosynthetic bacteria (PSB) were used to recover from VFAs inhibition (pH 6.0) of an anaerobic digestion system. After adding PSB for 12 days with and without light condition, the methane content recovered from 33.3% to 60.5% and from 32.1% to 59.3%, respectively; the pH increased to 7.1 and 6.8, respectively, the system alkalinity rapidly increased to 2238 and 1921 mg/L, respectively; the sCOD decreased from 5600 to 995 mg/L and from 5575 to 2025 mg/L, respectively; and the contents of formic acid, acetic acid, propionic acid and total VFA were greatly reduced. Microbial analysis found that PSB bioaugmentation could maintain microbial diversity of the system. PSB bioaugmentation could effectively relieve acids accumulation and stimulate methane production especially under light condition. It is also found that light could accelerate recovery with or without bioaugmentation.

Removal of contaminants of emerging concern by continuous flow solar photo-Fenton process at neutral pH in open reactors

For the first time, the operational feasibility of the solar photo-Fenton process at neutral pH in continuous flow has been tested for three consecutive days. The aim of the treatment was to remove of contaminants of emerging concern (CECs) from wastewater treatment plant secondary effluents. To this end, a 5 cm-deep raceway pond reactor was run in continuous flow mode and the degradation of the CECs present in real secondary effluents was monitored at their natural concentrations. To keep dissolved iron at neutral pH, ethylenediamine-N,N′-disuccinic acid (EDDS) was used to form the complex Fe(III):EDDS as an iron source for the photo-Fenton reactions. At pilot scale the effects of the Fe(III):EDDS molar ratio (1:1 and 1:2) and hydraulic residence time (HRT) (20 and 40 min) on CEC removal were studied. The best operating condition was 20 min of HRT, giving rise to a treatment capacity of 900 L m−2 d−1 with CEC removal percentages of around 60%. The reactant concentrations were 0.1 mM Fe(III):EDDS at a 1:1 M ratio and 0.88 mM H2O2. Under these operating conditions, the short-term stability of the process was also demonstrated, thus pointing out the potential of this solar technology as a tertiary treatment.

Treatment of domestic wastewater containing phosphate using water treatment sludge through UASB–clariflocculator integrated system

In the present study, treatment of low-strength synthetic wastewater through upflow anaerobic sludge blanket (UASB)–clariflocculator integrated system was carried out. Synthetic wastewater containing sucrose as a carbon source and phosphate as a nutrient was passed through the UASB reactor followed by clariflocculator. Water treatment sludge (WTS) was used as a coagulant in the clariflocculator. Box–Behnken design methodology with response surface methodology was used for optimizing the parameters including WTS dose, hydraulic retention time (HRT) and pH of UASB reactor. The phosphate removal was considered as a response. The observed values of responses were fitted by using second-order polynomial to compute the model. The suitability of this second-order polynomial model was checked by performing ANOVA test. Fisher’s test was done to analyze the significance of each factor and interactions between each other. With this methodology, the optimum operational condition of integrated system was obtained at 20 g/L as a WTS dose, HRT 7.68 h and pH 9. The UASB–clariflocculator integrated system removed 72.5% of phosphate at this optimum condition, whereas the phosphate removal through UASB reactor alone was obtained in the range of 8–20% only. The results suggested that water treatment sludge can be used as a coagulant to enhance the removal of phosphate from UASB reactor effluent treating low-strength wastewater and integrated system can be considered as a promising alternative of conventional system for the removal of nutrient from the effluent of UASB reactor.

Effect of Rice Bran on Continuous Organic Waste Decomposition Processes

The mirobial decomposition process of househole waste, mainly food waste, is considered an environmentally friendly way to treat organic wastes. However, there are some problems which often occur, such as low conversion rate and bad smell generation, especially in the early stage of continuous operation systems. Rice bran has been known empirically as an acclerator or improving material for the microbial decomposition process of organic wastes. Unfortuantely, little information about the detailed findings has been obtained so far.&#x0D; &#x0D; This study intended to analyze the effect of rice bran as an activating agent in organic waste decomposition in order to minimalize the problems. Firstly, the effect of rice bran was confirmed. Reactor weight, temperature, moisture content, pH, and microbe number were measured and used as the parameters to confirm the effect of rice bran addition in the decomposition process. It was observed that the total waste reduction during the process was larger in the case of rice bran addition than that of the blank, i.e. without rice bran addition. The other parameters also showed similar tendencies, indicating that rice bran is surely capable of activating the decomposition process. Then, the growth accelerating effect for microorganisms in the composting process was examined by a cultivation test using trypticase-soy liquid medium. The microbe number in the medium with rice bran addition was higher than the medium without rice bran.&#x0D; &#x0D; Secondly, the factors contributing this effect were searched. Although we could narrow down the number of candidate constituent, among them magnesium was one of the major candidates, the precise identification was not possible, possibly because the effect of each nutrient on the microbes varies depending on the kind of microbial strain, and not a single but a combination of multiple nutrients may cause this effect. However, it was confirmed as a whole that rice bran shows a good influence on the growth of many micorbes in the composting process and accelerates the performance of decomposition.&amp;nbsp;

Less biomass and intracellular glutamate in anodic biofilms lead to efficient electricity generation by microbial fuel cells

BackgroundUsing a microbial fuel cell (MFC), we observed that a complex microbial community decomposed starch and transferred electrons to a graphite felt anode to generate current. In spite of the same reactor configuration, inoculum, substrate, temperature, and pH, MFCs produced different current and power density. To understand which factor(s) affected electricity generation, here, we analyzed a complex microbial community in an anodic biofilm and fermentation broth using Illumina MiSeq sequencing and metabolomics.ResultsMicrobial biomass on the anode was lower in MFCs generating more electricity (0.09–0.16 mg cm−2-anode) than in those generating less electricity (0.60–2.80 mg cm−2-anode), while being equal (3890–4196 mg L−1-broth) in the fermentation broth over the same operational period. Chemical oxygen demand removal and acetate concentration were also similar in fermentation broths. MFCs generating more electricity had relatively more exoelectrogenic bacteria, such as Geobacter sp., but fewer acetate-utilizing Methanosarcina sp. and/or Lactococcus sp. in anodic biofilms. Accordingly, anodic biofilms generating more electricity presented higher levels of most intracellular metabolites related to the tricarboxylic acid cycle and a higher intracellular ATP/ADP ratio, but a lower intracellular NADH/NAD+ ratio. Moreover, the level of intracellular glutamate, an essential metabolite for microbial anabolic reactions, correlated negatively with current density.ConclusionMicrobial growth on the anode and intracellular glutamate levels negatively affect electricity generation by MFCs. Reduced formation of anodic biofilm, in which intracellular glutamate concentration is 33.9 μmol g-cell−1 or less, favors the growth of acetate-utilizing Geobacter sp. on the anode and improves current generation.

Influence of aeration rate and reactor shape on the composting of poultry manure and sawdust

ABSTRACTTo achieve successful composting, all the biological, chemical, and physical characteristics need to be considered. The investigation of our study was based on various physicochemical properties, i.e., temperature, ammonia concentration, carbon dioxide concentration, pH, electrical conductivity (EC), carbon/nitrogen (C/N) ratio, organic matter (OM) content, moisture content, bacterial population, and seed germination index (GI), during the composting of poultry manure and sawdust for different aeration rates and reactor shapes. Three cylindrical-shaped and three rectangular-shaped pilot-scale 60-L composting reactors were used in this study, with aeration rates of 0.3 (low), 0.6 (medium), and 0.9 (high) L min−1 kg−1 DM (dry matter). All parameters were monitored over 21 days of composting. Results showed that the low aeration rate (0.3 L min−1 kg−1 DM) corresponded to a higher and longer thermophilic phase than did the high aeration rate (0.9 L min−1 kg−1 DM). Ammonia and carbon dioxide volatilization were directly related to the temperature profile of the substrate, with significant differences between the low and high aeration rates during weeks 2 and 3 of composting but no significant difference observed during week 1. At the end of our study, the final values of pH, EC, moisture content, C/N ratio, and organic matter in all compost reactors were lower than those at the start. The growth rates of mesophilic and thermophilic bacteria were directly correlated with mesophilic and thermophilic conditions of the compost. The final GI of the cylindrical reactor with an airflow rate of 0.3 L min−1 kg−1 DM was 82.3%, whereas the GIs of the other compost reactors were below 80%. In this study, compost of a cylindrical reactor with a low aeration rate (0.3 L min−1 kg−1 DM) was more stable and mature than the other reactors.Implications: The poultry industry is growing in South Korea, but there are problems associated with the management of poultry manure, and composting is one solution that could be valuable for crops and forage if managed properly. For high-quality composting, the aeration rate in different reactor shapes must be considered. The objective of this study was to investigate various physicochemical properties with different aeration rates and rector shapes. Results showed that aeration rate of 0.3 L min−1 kg−1 DM in a cylindrical reactor provides better condition for maturation of compost.

Effect of basic oxygen furnace slag addition on enhanced alkaline sludge fermentation and simultaneous phosphate removal

This study presents a promising approach that enhances the sludge fermentation by using basic oxygen furnace (BOF) slag as an alkaline source for the first time. BOF slag added to the reactors could maintain a stable alkaline condition due to continuous release of Ca(OH)2 from slag. The reactor pH could be adjusted to a target value by the choice of the BOF slag dose. Concentrations of soluble chemical oxygen demand (sCOD) and short-chain carboxylates (SCCs) were substantially increased in the presence of BOF slag. At a BOF slag mass to sludge volume ratio of 1/10 g slag/L sludge, the reactor pH was maintained at 10 and the concentration of SCCs produced was the highest (i.e., 3510 mg COD L−1 from 14,000 mg VS L−1 of sludge mixture), followed by B/S ratios of 1/20, 1.50, 1/5, and 1/2.5 g slag L−1 sludge with reactor pH of 9.4, 8.9, 10.5, and 11, respectively. Our data suggest that the pH value that best facilitates the degradation of sludge into SCCs and inhibit the conversion of SCCs into biogas is around 10. Interestingly, compositions of the accumulated SCCs varied greatly depending on the BOF slag dose. BOF slag showed phosphorus removal ability due to enhanced precipitation of Ca-PO43--P complexes, which significantly lowered PO43− concentration of the reactor effluent.